Method of magnetizing magnets for a repulsion type of suspension



7 March 18, 1969 J. w. MlLLlGAN METHOD OF MAGNETIZING MAGNETS FOR AREPULSION TYPE OF SUSPENSION Original Filed Aug. 14. 1961 Sheet of 2INVENTOR.

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March 18, 1969 J. w. MILLIGAN METHOD OF MAGNETIZING MAGNETS FOR AREPULSION TYPE- OF SUSPENSION firiginal Filed Aug. 14.

Z of 2 Sheet R a m 0 T Wm B WM W mm T I N w W W Mm a C WH n H m s m US Ao A n 9 6% n fl Q Q iilwfiii/ m Q h u. ilillk. .LHHI m :u I. 4 3 7 I x51AIR-v BY {2%, /M@% mwuy United States Patent 3,434,084 METHODOF'MAGNETIZING MAGNETS FOR A REPULSION TYPE OF SUSPENSION James W.Milligan, West Lafayette, Ind., assignor to Duncan Electric Company,Inc., a corporation of Indiana Original application Aug. 14, 1961, Ser.No. 131,286. Divided and this application Oct. 23, 1965, Ser. No.504,257

U.S. Cl. 335-284 Int. Cl. H01f 7/20, 13/00 Claims ABSTRACT OF THEDISCLOSURE This application is a division of Ser. No. 131,286 entitledMagnetic Repulsion Type of Suspension, filed Aug. 14, 1961, stillpending.

Various pieces of apparatus have shafts which must be rotatable with avery small amount of friction, often with a requirement of remainingstable for years. A common example is the watt-hour meter (the familiarelectric meter of the home). Another example is a gyroscope. In

the past, various structures have been devised for reducing thefrictional drag upon a shaft of such a structure. One of these,especially suitable when the shaft is substantially vertical, is tosuspend it magnetically so that the weight of the rotor does not ride ona thrust bearing with its attendant frictional drag, and danger ofincreasing drag due to dirt or wear. Although such magnetic suspensionshave been successfully used, they have been subject to recognizeddefects.

In casual theory, magnetic suspension or support would seem to be idealfor reducing the frictional drag of the shaft supports. Upon morecareful examination, the theory has drawbacks. One is lack of lateralstability. If the rotor moves slightly off center there results amagnetic side thrust. This necessitates a centering bearing, which inturn reintroduces rotational drag on the shaft, wear problems, etc.Also, past magnetic suspensions have been too delicate or soft. A changein positioning can change the application of forces to the meter disk,affecting the accuracy of meter operation. In a sof suspension, a minutechange of magnetic strength produces a relatively great change ofpositioning. Also, in actual practice, there have been other faults,such as sensitivity to temperature changes and to external magnetfields. Also, if the magnetic fields from the two coacting pole facesboth have any unevenness in the strength about the axes, this will actto produce unwanted locking forces, causing the shaft to seek aparticular angular position and resisting the start of rotation.

An object of the present invention is to provide a structure forelectric meters or the like which will ameliorate the problemsencountered with prior art devices and methods. Through the use of theinvention, the shaft is stably supported and the decentering side thrustintroduced by magnetic fields of the support, when other forces causeminor decentering, is relatively low. As a result, the extent to whichthe centering bearings must hold the shaft "ice bearing is lessened,with a corresponding reduction of wear and fractional drag in the shaftbearings. In fact, the support by magnetic repulsion with centering alsoby magnetic repulsion, in accordance with one form of my invention, isdesigned to resist such side-shifting of the shaft as may be introducedby other factors. Also, as a result of the design, and of the highlystable nature of the magnetic material, especially as used, externalinfluences have amazing little effect.

This is all accomplished with a repulsion type magnetic suspension whichhas an inherent advantage of magnetically expelling any magnetic dirtwhich would gather in the gap of a magnetic suspension of the attractingpoles type.

Further objects and advantages of my invention will become apparent fromthe following description taken in conjunction with the drawings inwhich:

Designation of figures FIGURE 1 is an elevational sectional view of aportion of an electric watt-hour meter embodying my invention;

FIGURE 2 is mainly a face view of one magnet, being also a section asviewed at line 2-2 of FIG. 1;

FIGURES 3 and 4 are vertical sectional views of modified constructions;

FIGURE 5 is a sectional view of a fixture for magnetizing theshaft-mounted magnet of FIG. 1;

FIGURE 6 is a vertical sectional view of alternative apparatus formagnetizing the magnets of FIGS. 1 and 3;

FIGURE 7 is a horizontal sectional view taken along the line 77 of FIG.5.

FIGURE 8 is a sectional view of apparatus for magnetizing the shaftmagnet of FIG. 4.

FIGURE 9 is a sectional view of an apparatus for magnetizing the ringmagnet of FIG. 4.

General description Although the foregoing disclosure offered for publicdissemination is detailed to insureadequacy and so aid understanding,this is not intended to prejudice that purpose of a patent which is tocover each new inventive concept therein, no matter how others may laterdisguise it by variations in form or additions or further improvements.The following claims are intended as the chief aim toward this purpose,as it is these that meet the requirement of pointing out the parts,improvements, or combinations in which the inventive concepts are found.

Referring to FIGURES 1 and 2., there is illustrated a portion of anelectric watt-hour meter having a frame generally 10 and a vertical,rotating, shaft generally 11, carrying a disk 11'. The associatedelements of the meter such as driving and retarding magnets are wellknown but are not shown. Their structure and relationship to theillustrated device will be understood by those skilled in the art.

The upper end of the shaft 11 is guided by a pin 16 running in agraphite bearing 24. The weight of the shaft is suspended by magneticrepulsion between magnets 30 and 35, rotor magnet 30 being fast on shaft11, and stator magnet 35 being fixed in stud or holder 13.

- Magnets 30 and 35 are substantially identical. In accordance with thepresent invention their 'four permanent magnet pole faces all faceaxially, are close together, and of the same area, and like poles aredirectly opposite one another. Thus the outer pole faces 38 and 41(having the same polarity) are of the same area as the inner pole faces39 and 42, and the grooves or spaces 40 and 43 each between the two polefaces of one magnet, are quite narrow, in fact narrower in theillustrated form than either pole face. This arrangement, with propermagnetization to support the rotating element with the illustrated gapbetween magnets 30 and 35 (about .05") provides a very stiff suspension,and one in which the magnetic side thrust resulting from minutedisplacements is very small. During normal operation, pin 19 andgraphite ring 25 (having a running fit with pin 19) confine the lateralmovement of magnet 30 to such minute lateral displacements that magneticside thrust is extremely low.

Detailed description Frame (only outstanding bosses of which are shown)carries an upper mounting stud 12 and a lower mounting stud 13. Each ofthe studs are circular in a transverse cross-section. They are receivedin suitable openings in the frame bosses 10 and held in place by capscrews 14. Stud 12 has an axial bore or cavity 15 of cylindricalconfiguration with a small rod or centering pin 16 extending along theaxis of the bore. Pin 16 is held in place by a die-cast plug 17.Similarly stud 13 has a bore or cavity 18 and a rod or centering pin 19along the axis thereof which rod is held in place by plug 20. Pins 16and 19 are accurately centered by virtue of being held centered whileplugs 17 and 20 are die-cast.

At each end of shaft 11 are cavities 22 and 23 respectively. Cavities 22and 23 are cylindrical in shape with their cylindrical axes coincidingwith the axis of shaft 11. Secured in one end of shaft 11 at the mouthof cavity 22 is a graphite bearing 24 having the opening aligned withthe axis of shaft 11, in which opening pin 16 is journaled. Acorresponding bearing 25 is secured to the opposite end of shaft 11 atthe mouth of cavity 23.

Near the lower end of shaft 11 is a knurled section 27 these cooperatingto ensure dependable positioning of magnet 30. While rotor magnet isheld accurately centered on the shaft 11, binding metal 29 is die-castin place. Alternatively (as in FIG. 3) the magnet 30 may be cemented toa collar 29 with which centering is ensured by interfitting parts, andwhich snugly fits the shaft and is tightened thereon by setscrews.

Lower magnet is bound to stud 13 by die-cast metal 36, which may beapplied at the same time as plug 20.

Magnets 30 and 35 are identical. Magnet 35 includes an outer annularpole face 38 and an inner annular pole face 39. As illustrated, the twopole faces are separated by a groove 40. Likewise magnet 30 has an outerannular pole face 41 and an inner annular pole face 42 separated by agroove 43. The grooves and 43 are valuable, but not always essential. Itwill be noted in FIGS. 1 and 2 that pole faces 39 and 42 are wider thanpole faces 38 and 41. This is done so that the area of pole faces 39 and42 is approximately equal to the area of pole faces 38 and 41,respectively.

Although best results are attained with approximate equality in area,perfection is not essential. However, any departure from area equalityis believed detrimental or wasteful. With more than somewhere around a40% difference in area between the outer pole faces and the respectiveinner pole faces, the added increments of metal of the larger pole willbe functioning mainly in the inferior manner of a magnet having only oneof its poles in a repelling position.

Magnets 30 and 35 are magnetized so that the outer pole faces 41 and 38are of the same polarity and the inner pole faces 42 and 39 are both ofthe opposite polarity. In the illustrated embodiment the former aredesignated north poles while the latter are designated south poles.However, the polarity of both magnets could be reversed withoutsignificance depending upon the choice of the manufacturer. The use ofthe designations N and S in the drawing is merely to illustrate therelative polarity of the two pole faces. It is intended that the magnets30 and 35 have the same relative strength at all angles of rotationabout the axis of shaft 11. Thus the magnetic field about either one ofthe magnets is roughly that of a semi-toroid, with the plane of polefaces 41 and 42, for example, approximately bisecting the toroid, andbeing normal to the axis about which the toroid was formed. The pins 16and 19 which have been used are 0.019 inch in diameter. Because of theirsmall size, zero or very small bearing load, and their being journaledin the graphite bearings 24 and 25, the frictional drag to the rotationof shaft 11 is extremely small. During normal operation, these pinsresist any side thrust so that lateral shifting is extremely small.However, the structure is adequately protected in another way againstshock damage, as in shipment. Thus with the ends of shaft 11 received incavities 15 and 18, the shaft is thereby restrained against excessivelateral movement.

There is also protection against excessive axial displacement, whichwould otherwise be likely to occur in shipment. Thus pins 16 and 19 havesuitably small clearance, such as .010" to .015", with the ends ofcavities 22 and 23. The latter may be formed by an inserted end stopbearing to allay fears of purchasers who know ,such end stops have beenneeded heretofore and may not at first have confidence in theexceptional degree of insensitivity to temperature changes hereachieved.

Magnetizing fixture and method A fixture for magnetizing magnet 30 isillustrated in FIGURE 5. It includes a frame generally 48 having anupper arm 49 and a base arm 50. An electro-magnet, generally 51, ismounted on base arm 50. It includes a core 52 of sof magnetic material,the upper portion of which is annular in shape and defines annular poleface 53. A casing 54 of soft magnetic material surrounds core 52 anddefines an annular pole face 55. Pole faces 53 and 55 lie in a commonplane are are separated by a gap 56. The configuration of pole faces 55and '53 corresponds to the configuration of pole faces 41 and 42,respectively. Between core 52 and casing 54 in gap 56, (in theillustrated form) are the windings of a coil 57 energized through a pairof wires 58. The projecting portion of shaft 11, immediately below poleface 42 fits snugly into bore 59 of core 52 to center magnet faces 41and 42 with the corresponding faces 53 and 55 of the magnetizer.

It may be noted in this connection that the provision of grooves 40, 43is quite desirable in reducing the need for extremely precise centeringof the magnet pole faces on the pole faces of the magnetizer. It hasbeen found tolerable, with grooves 40 and 43 provided, to have the bore59 of a diameter .002 larger than the diameter of the interfittingportion of shaft 11. The limit has not been determined.

It is also important that the windings of coil 57 extend quite close tothe plane of the magnetizer pole faces 53 and 55. Likewise the coilshould be concentrated very close to this area so that a largeproportion of the total ampere-turns will be in this area. It has beenfound possible to saturate the permanent magnets by using 11,000 to12,000 ampere turns in a coil extending from .005 to .150" from theplane of the faces. The turns of the coil should be firmly boundtogether, as by high temperature shellac also used for coating the wirefor insulation.

With these various contributing factors, it has been found that magnetscan be produced of exceptionally high magnetic uniformity about the axisand with very nearly the maximum pole face strength of which a givenmagnet is capable. By pole faces is, of course, meant the faces at theends of that portion of the main magnetizing flux path lying within thepermanent magnet. In the case of magnet 30 these would obviously befaces 41 and 42 since they are in contact with the iron of themagnetizing unit. To distinguish these faces more clearly from facesadjacent to them, where some leakage flux may escape, each of the facessuch as faces 41 and 42 can be desig nated a face of greatestconcentration of flux of that faces polarity or a face containing apolarity center.

Stabilizing magnetic knock-down As is Well known in regard to magnets ingeneral, after magnetization they should be subjected to a partialknockdown or demagnetization for stabilization purposes. This may beaccomplished in the case of the illustrated magnets in conventionalmanner as by insertion in an alternating field of constant strength adremoval therefrom.

Preferably wires 58 are connected to a source of flash current, e.g. acurrent of high intensity and short time .duration. Such devices arewell known in the art, and their current may be derived from condenserdischarge. The magnet to be energized, for example magnet 30, is placedin position in the electromagnet. A flash of heavy mag netizing currentis passed through coil 57 to magnetize the magnet to saturization.Thereafter, if stabilization is ,to occur on the same fixture, ademagnetizing current, which may be of reverse polarity, or oscillatory,of much less strength is passed through coil 57 to partially demagnetizeand stabilize the magnet. The residual magnetism of the two magnetsshould be such as to support the desired weight with the desired axialdistance between the corresponding faces e.f. faces 38 and 41, of themagnets when in use. In a particular specific embodiment the strengthsof the magnetic fields (and of the demagnetizing current) required toachieve this spacing fairly closely can be readily determinedempirically. Also, a special demagnetizing set up can be provided togive a final increment of demagnetization, progressively increasing thestrength of successive spaced impulses until the exact desired residualflux value is attained.

Demagnetization with compensation The plane defined by the pole faces 38and 39 and that of pole faces 41 and 42 should be parallel to each otherand normal to the axis of shaft 11. In order to obtain the advantage ofless expensive manufacturing operations, some minute errors may beencountered. To minimize their effect, the following novel method formagnetizing and stabilizing magnet 30 can be employed.

Referring to FIGURE 5 there is on arm 49 a plug 63 carrying a pin 64which is receivable in bearing 24 (FIG. 1) of shaft 11. Plug 63 ismounted in arm 49 so as to be vertically movable with respect to thearm. Pin 64 and bore 59 are positioned so that their axes are coincidentand very accurately normal to the plane defined by pole faces 53 and 55.In other words, the faces 53 and 55 are accurately formed as surfaces ofrevolution about the axis of pin 64 and bore 59. When magnet 30 andshaft 11 are first inserted into the fixture, plug '63 is raised so thatpin 64 does not enter the bearing in the top end of shaft 11. If theaxis of shaft 11 is not normal to the plane of pole faces 41 and 42,shaft 11 will be cocked off to one side as illustrated in dotted linesat 11 The magnet 30 will assume a position at which pole faces 41 and 42are in full face-to-face contact with pole faces 55 and 53. The initialmagnetizing current is now passed through coil 57. After the initialmagnetizing of the magnet, shaft 11 is moved to a position at which pin64 will enter the bearing in the top of the shaft. In production, aquicker or more automatic device will probably be provided for centeringthe shaft on its proper axis. In any event, the shaft 11 is now held inthe position illustrated in full lines in FIG. 5. While the movement ofshaft 11 to achieve this repositioning may be very small, if enough tobe significant it will result in some loss of the face-to-face contactbetween the pole faces of the magnetizing magnet 51 and the pole facesof the magnet 30. With the shaft 11 held in the full line position,except that magnet 30 rests on magnet 51 as indicated by the arrow, thede-magnetizing current now is passed through coil 57. The areas ofmagnet 30 fully in contact with the poles of electro-magnet 51 will bede-magnetized the greatest amount. To the extent that there is an airgap between other portions of the pole faces 41 and 42 with respect tothe pole faces 55 and 53, respectively, a lesser amount ofde-magnetization will occur. The larger the gap, the smaller will be theamount of demagnetizing of that portion of magnet 30. Thus, when theshaft with its magnet is mounted as illustrated in FIG. 1, to the extentthat there is a cocking of magnet 30 on shaft 11 with one side of magnet30 being closer to magnet 35 than is the opposite side of magnet 30,that one side of magnet 30 (the close side) will have a smaller residualmagnetism. The greater residual magnetism at the area of greatestspacing will tend to compensate for this greater spacing, and nearequality of magnetic field along a perpendicular plane results.

Although this compensating demagnetization is available if needed,present experience indicates that sufficiently accurate mounting ofmagnets 30 and 35 can be achieved in production so that it will not 'berequired.

Magnetizer for shaftless magnets In FIG. 5 magnet 30 was centered byinterfitting of its shaft 11 with bore 59.

FIG. 6 shows a construction suitable for magnetizing magnets which arenot mounted on shafts. The construction of the electromagnet portion issimilar to that of FIG. 5, except that instead of having a bore 59 intowhich a shaft extends it is provided with a centering dowel 65 whichsnugly fits into the bore or central aperture of the magnet to bemagnetized.

Air-cleaning of magnetizers Preferably the magnetic cores 52 areprovided with slots 66 along their cylindrical faces, these slotsextending axially as seen best in FIGS. 5 and 6. The coil lead wires mayextend through one such slot. As seen in FIG. 7 there may be severalsuch slots spaced around the core 52. Preferably these slots communicatewith a hose 66' for supplying compressed air. This air will help keepthe pole faces of the magnetizer clean by blowing past the outside ofcoil 57 which is tightly mounted on core 52 but has a slight clearancewith shell 54.

Magnetic suspension with repulsion centering FIG. 4 illustrates thelower portion of a shaft 67 generally corresponding to shaft 11. Theupper end of shaft 67 (not shown) might be mounted in a bearingstructure corresponding to the upper mounting of shaft 11. Projetcingfrom the bottom of shaft 67 is a pin 68 which may be quite stiff. It isshorter and may be of larger diameter than pins 16 and 19. Pin 68extends into a cavity 69 in a support block 70. Support block 70 wouldbe mounted on a suitable frame such as frame 10' of FIG. 1.

Above cavity 69 is an enlarged cavity 71 at the bottom of which isseated a graphite bearing 72. Bearing 72 has an axial opening 73 toreceive pin 68 quite loosely. Surrounding the bottom end of shaft 67 isa support magnet 74 which may be identical to magnet 35 of FIG. 1.Magnet 74 has an outer annular pole face 75 and an inner annular poleface 76, corresponding to pole faces 38 and 39, respectively. The twopole faces 75 and 76 may be separated by a groove 77. I

Rotor magnet 82 is secured about a knurled section 80 of shaft 67 bymetal 81 die cast in situ. Magnet body 82 is cylindrical in shape. Itsbottom plane is provided with an outer annular pole face 83 and an innerannular pole face 84 which may be separated by a groove 85. The shapeand size of pole faces 83 and 84 correspond to those of pole faces 75and 76. 7

About the periphery of magnet body 82 adjacent the upper end thereof area pair of circumferential pole faces 87 and 88, which may be separatedby a groove 89. An annular magnet 90 has a pair of inner circumferentialpole faces 91 and 92 separated by a groove 93.

.Pole faces 87 and 91 are of one polarity while pole faces 88 and 92 areof the opposite polarity. Thus the magnetic field between the uppermagnet of body 82 and the ring magnet 90 is such that these magnets actto repel each other and will serve to center shaft 67 to coincide withthe vertical axis of pole faces 91 and 92. Pole faces 83 and 75 also areof one polarity, with pole faces 76 and 84 being of the oppositepolarity. Thus the bottom magnetic portion of magnet body 82 will besupported by the repelling magnetic force between that magnet body andmagnet 74. If the forces applied to the rotating element of whichspindle 67 is a part are fairly light or well balanced as to lateralforces on spindle 67, pin 68 will presumably never touch bearing 72during normal operation, and ordinary friction will be zero.

Similar results are expected from a single pair of nested magnets withfaces of conical shape. Thus each magnet is to have both of its faceslying in a surface of revolution about the axis which would be generatedby a line olique to the axis. The groove between the poles of one magnetshould be displaced from the other along a cone perpendicular to thecones of the faces. The outer magnet may have its inner face extended tothe same internal diameter as the opposing inner face, and its outerface extended to the horizontal plane of the outer diameter of theopposing outer pole.

Stator magnet 74 may be magnetized on an electromagnet such as thatillustrated in FIG. 5. FIGURES 8 and 9 respectively illustrate thefixtures for magnetizing magnet body 82 and ring magnet 90. Referring toFIG. 8, there is an annular core 95 of soft magnetic material having aslot therein to receive the electrical windings 96. At the same time theslot holding winding 96 defines a pair of circumferential pole faces 97and 98. A pair of annular rings 99 and 100 are positioned at oppositesides of core 95. The rings 99 and 100 are made of anelectro-conductive, non-magnetic, material such as copper.

The bottom face of magnet body 82 is magnetized by an electro-magnetwhich includes a core 102 having a slot in the upper face thereof toreceive winding 103. The slot receiving winding 103 together with theaxial opening 104 define annular pole faces 105 and 106 in juxtapositionto pole faces 83 and 84, respectively. Windings or coils 96 and 103 aresuitably connected to a source of flash current 107 such as that used toenergize coil 57 of the embodiment of FIG. 5. As in the embodiment ofFIG. 5, coils 96 and 103 are first energized by a relatively largeimpulse current of one polarity to magnetize magnet body 82 tosaturation. Thereafter a smaller impulse current of reverse polarity maybe passed through coils 96 and 103 to partially de-magnetize the magnetbody. Coils 96 and 103 have been shown connected in series to indicatethat they are energized exactly in unison, so that neither willadversely affect the magnet the other magnetizes.

FIG. 9 shows the fixture for magnetizing magnet 90. A generallycylindrical core 109 has a slot therein to receive a winding 110. Theslot within which winding 110 is positioned defines a pair of peripheralpole faces 111 and 112 generally corresponding to pole faces 91 and 92of magnet 90. A pair of cylindrical copper disks 103 and 104' arepositioned at opposite sides of core 109. Winding 110 is connected tothe source of flash current 107. Initially it is energized by arelatively high current to saturate magnet 90. Thereafter it may beenergized by a somewhat lower current of opposite polarity to partiallydemagnetize magnet 90. As made clear by my application resulting inPatent No. 3,114,582, rings 99, 100, 103' and 104', with the flashmagnetizing current indicated, substantially confine the magnetizingflux to flux entering the pole faces perpendicularly, this effect beinginevitably achieved in FIG. 6 by the contact of the magnetized andmagnetizing faces in a closed magnetic circuit.

Magnetic considerations To achieve the objects of my invention to bestadvantage it is important as has been noted that the width of grooves 40and 43 (as measured along a radial line) be quite small. The correctdimension for optimum results may vary, but it now appears that for safeachievement of these results the width of the gaps 40, 43 should not bein excess of 3 mm., as it is believed that size would be inferior to thedimensions given below. Magnets 30 and 35 as now most thoroughly testedhave an overall diameter .564 and a bore diameter .156", the width ofgrooves 40 and 43 as measured along a radius is .043". Pole face 39 hasa radial dimension of .107" and pole face 38 has a radial dimension of.054. The magnets as measured along the axis of shaft 11 may be .187"thick. The magnets may be made of one of the materials well known to theart for forming high coercive permanent magnets, such as one of thealloys sold under the trade name Alnico. A very high coercive material(at least 650 oersteds) should be used. Present preference is a moldedcomposition of Alni-co VII powder bound by a stable, thermosetting resinwith a high heat-distortion temperature. Although the magnetizedsuspension of FIG. 4 has not yet been constructed, the smallness ofmagnetic side thrust encountered with the FIG. 1 type of suspensionsuggests that the FIG. 4 type may achieve complete magnetic stability,even though that has seemed impossible heretofore. At least, it willapparently achieve a condition of mini-mum magnetic sidethrust caused byminute eccentricity, and if this is all it achieves it should have thesame type of centering pin as in FIG. 1. Grooves 89 and 93 should alsobe not over 3 mm. in width (axial dimension) and preferably as small aspractical, e.g. .04.

The FIG. 1 form of the invention has been found exceedingly satisfactoryfor supporting 16 gram rotating elements, such as single phase meterrotors. On 32 gram elements (2 discs) greater magnetic side thrust isdeveloped by minute eccentric displacement, but it is still withintolerable range, and the suspension is also satisfactory for thisheavier rotor. In fact this is the planned first commercial use.

Maintaining a small overall diameter for the magnets is important.Partly this is desirable for reasons of economy and compactness. Inaddition it shortens the torque arm of any force resulting from lack ofperfection in uniformity, thereby making such nonuniformity lessobjectionable than if it had a longer torque arm, or long leverage. Whenpossible the external diameter of the magnets should be kept at least assmall as threefourths inch. Where greater lifting force is required itwould be better to use more pairs of magnets axially separated than touse one pair of magnets of larger diameter.

The outside diameter is kept at a minimum by having both pole faces ofone magnet of the same area, and by keeping the separating groove smallas measured along a radius; both the factors being desirable for otherreasons also. By a resin of high heat distortion temperature is meantone which will withstand at least 250 F. without significant distortionby a moderate applied force. For example, five pounds applied through adiameter ball should not leave a depression over .010".

It is important that the stabilizing demagnetization be to a degree suchthat when the magnets are moved into the closest proximity permitted bythe physical dimensions of the parts, they will have no furtherpermanent demagnetizing effect. At present, a demagnetizing field ofabout 700 oersteds is used, and even face to face contact of the magnetswould have no further effect although such contact is prevented.Demagnetization will also determine the length of the axial gap betweenmagnets when a given load is supported. At present an axial gap of about.050" is used with a 35 gram total rotor weight (including the rotormagnet). About .060 to .065" is planned for an 18 gram rotor, usingsmaller magnets. It will be observed that these axial gaps are longerthan the width of the groove separating the magnet faces, by asubstantial percentage. A gap slightly shorter than the groove width hasalso been used, but relative side thrust was increasing and much lessthan this should apparently be avoided. In other words, axial gap shouldbe at least of the order of approximately equal to the groove width (orseparation of the pole faces, if no groove).

Although mention has been made as to each magnet that the separation ofits magnetic poles should not be over 3 mm., it is believed that infact, it should be as little as is practicable. Making it smaller thanabout .04" appears to be difiicult, however, in view of the need to usea large number of ampere turns adjacent to the plane of the pole facesof the magnet being magnetized. Hence, a dimension of about .04" is atpresent preferred.

Alnico VII should be unoriented (isotropic) and has a composition inpercentage by weight of:

Precision die-casting It is, of course, extremely important that theplane of pole faces 38 and 39 lie perpendicular to the axis of holder13. Features illustrated in FIG. 1 facilitate achieving this inproduction.

One of the important features is the provision of a deformable annularrib 120 close to the cavity 18 of body 13. In the course of die-casting,the die which engages the pole faces 38 and 39, and which also fitswithin the central bore of magnet 35 for centering this magnet, ispressed with great force, such as a hundred pounds, toward the portionof the die which holds body 13 accurately centered therein. This forceis enough to upset or deform rib 120, the body 13 being of aluminum.Thus, if there is any minute irregularity which causes uneven spacingbetween magnet 35 and body 13 the annular rib 120 will be deformed toaccommodate itself to this irregularity. While the parts are thus heldin proper relationship the die-casting metal will be injected. The rib120- serves to seal the flowing metal from penetrating into the cavity18 in the vicinity which will later be occupied by the shaft 11.

In order for the die-cast portion 36 to be formed by the same injectionas the plug 20, bore 121 is provided transversely through the body 13.Thus the metal can flow from one source to all of the points shown. ofcourse, the die member which holds magnet 35 is provided with anextension which forms the inner contour of the diecast metalconstituting the bottom portion of cavity 18.

Conclusion According to this invention an exceedingly stiff magneticsuspension is provided, without excessive side thrust upon minutelateral displacement. In addition, tests have shown that it hasamazingly low sensitivity to temperature changes. This suspension hasbeen used with a 32 gram rotor which moves axially only about .003" orless with a temperature variation from minus 40 C. to plus 90 C. This,of course, is far beyond the range to which watt-hour meters are likelyto be subjected. For comparison with one of the best prior magneticsuspensions it may be noted that with the same temperature variation avertical movement at least three times that here indicated would havebeen expected.

In addition the magnetic suspension of this invention has proved to beexceedingly immune to temporary or permanent magnetic change due toexternal magnetic fields to which it may be subjected either as a resultof intentional tampering or because of surge currents resulting fromlightning discharges striking the transmission lines. For example, withone prior commercial magnetic suspension of the repulsion type it hasbeen found that a readily available permanent magnet, when applied tothe external meter cover at the right place will so affect the magnetsof the magnetic suspension that they will allow the rotor to drop atleast .020", or until the magnetic faces engage one another, therebyintroducing great rotative friction. With the present invention, thesame permanent magnet similarly applied will cause only a drop of therotor of .004", or less.

What I here claim is:

1. The method of conditioning a permanent magnet on a shaft with a pairof coplanar pole faces generally normal to the axis of the shaft, andusing an electromagnet having coplanar pole faces, said method includingthe steps of: energizing the electromagnet with a magnetizing currentwhile the pole faces of the shaft magnet are in coaxial full facecontact with the pole faces of the electromagnet, and thereafterpositioning the shaft with its axis normal to the plane of theelectromagnet pole faces whereby any deviation from the right-angularrelationship between the shaft axis and the plane of the shaft magnetpole faces will result in a corresponding deviation between the plane ofthe electromagnet pole faces and the plane of the shaft magnet polefaces; and with the magnets so positioned, energizing the electromagnetwith a smaller demagnetizing current.

2. The method of conditioning a permanent magnet on a shaft with polefaces generally forming surfaces of revolution about the axis of theshaft and using an electromagnet having a correspondingly shaped poleface, said method including the steps of: energizing the electromagnetwith a magnetizing direct cur-rent of relatively high intensity whilethe faces of the two magnets are positioned in full face-to-facecontact; and thereafter energizing the electromagnet with a smallercurrent of reverse polarity while sai-d shaft is held in a positionabout which the face of the electromagnet is truly a surface ofrevolution, whereby any nontrueness of the permanent magnet face causesa differential positioning thereof with respect to the electromagnetface, and hence a differential knockdown of the permanent magnet.

3. The method of conditioning a permanent magnet on a shaft with polefaces generally forming surfaces of revolution about the axis of theshaft and using an electromagnet having a correspondingly shaped poleface, said method including the steps of: magnetizing the permanentmagnet with uniformity around the axis and partially demagnetizing it byenergizing said electromagnet while the permanent magnet is positionedby aligning the shaft selectively as to the electromagnet face wherebyany nontrueness of the permanent magnet face causes a differentialpositioning thereof with respect to the electromagnet face, and hence adifferential knockdown of the permanent magnet.

4. The method of magnetizing a permanent magnet having two pole facesslightly spaced apart'annularly comprising the steps of positioningface-to-face therewith an electromagnet, having two magnetizing polefaces matching those of the permanent magnet, and an energizing coilsubstantially annularly between the two magnetizing pole faces, and withthe energizing coil of the electromagnet extending substantially to aposition representative of a surface coinciding with the permanentmagnet faces and forming a continuation thereof, and causing a flashcurrent of heavy amperage to traverse said coil.

5. The method of magnetizing a permanent magnet having two pole facesslightly spaced apart annularly comprising the steps of positioningface-to-face therewith an electromagnet, having two magnetizing polefaces matching those'of the permanent magnet, and an energizing coilsubstantially annularly between the two magnetizing pole faces, and withthe energizing coil of the electromagnet extending at least as close asapproximately .005" to, and lying entirely within approximately .150" ofa position representative of a surface coinciding with the permanentmagnet faces and forming a continuation thereof and causing a flashcurrent of heavy amperage to traverse said coil.

References Cited UNITED STATES PATENTS 7/1941 Jurak 335-284 2/ 1960Weber US. Cl. X.R.

